With the reduction in size and weight of electronic and electric devices, there is an increasing demand for reductions in size and weight of electrochemical devices, such as secondary batteries. However, currently available electrochemical devices have a complicated internal structure, so that there is a limit to improvements in electrical capacity per a given volume of a device.
Complicated structure prevents improvements in reliability of electrochemical devices in some aspects. For example, a current-collecting tab or lead connected to an electrode may interfere with a homogeneous electrode reaction in the plane of the electrode. In the event that a cut section of the lead has metallic burrs that are larger than usual, an internal short-circuit may occur.
Electrochemical devices usually have an electrode plate assembly including a positive electrode, a negative electrode and a separator. The electrode plate assembly is either of a layered type or a wound type. A layered type electrode plate assembly is obtained by alternately layering positive electrodes and negative electrodes with separators interposed between them. Also, a wound type electrode plate assembly is obtained by winding a long positive electrode and a long negative electrode with a separator between them. Current-collecting tabs or leads are necessary for taking electricity out of such an electrode plate assembly without causing a short-circuit.
From the viewpoint of simplifying the internal structure of electrochemical devices, it has been proposed to cause a positive electrode to protrude from one side face of an electrode plate assembly and cause a negative electrode to protrude from the side face opposite the above-mentioned side face, in order to directly take out electricity from each side face without using tabs or leads.
For example, for batteries with a layered type electrode plate assembly, a technique of integrally joining protruded electrode plates of the same polarity with a metal member has been proposed (Japanese Laid-Open Patent Publication No. 2001-126707). Also, for batteries with a wound type electrode plate assembly, a technique of joining the core material of a protruded electrode plate of the same polarity with a plate-shaped current collector plate has been proposed (Japanese Laid-Open Patent Publication No. 2000-294222).
However, in such cases where the positive electrode is caused to protrude from one side face of the electrode plate assembly and the negative electrode is caused to protrude from the side face opposite the above-mentioned side face, the manufacturing process of the electrode plate assembly becomes complicated. Accordingly, electrode plate assemblies need to be produced one by one, thereby having a problem of being unable to manufacture a plurality of electrode plate assemblies at the same time.